A second package — like the first, shipped from Yemen — was discovered aboard a plane in England. It, too, was addressed to a Jewish organization in the Chicago area, although there was no immediate confirmation about its contents.

Several other cargo planes at airports along the Eastern Seaboard of the United States also were searched, and officials said no explosives were found. An Emirates Airlines passenger jet carrying cargo from Yemen was escorted from the Canadian border to New York City by two military fighter jets, U.S. officials said. They said it was a precautionary action.

President Barack Obama arranged to make a statement about the developments at the White House. Aides said he had been informed about a "potential terrorist threat."

"The president directed U.S. intelligence and law enforcement agencies and the Department of Homeland Security to take steps to ensure the safety and security of the American people, and to determine whether these threats are a part of any additional terrorist plotting," the White House said in a statement.

An FBI spokesman in Chicago, Ross Rice, said both suspicious packages had been sent from the same address in Yemen.

U.S. officials said they were increasingly confident that the packages were part of a plot by Yemen's al-Qaida branch, the same group responsible for an attempted bombing of a U.S.-bound airliner last Christmas. They spoke on condition of anonymity, citing the ongoing investigation.

Other officials, also speaking on condition of anonymity, said the package found in England contained a printer toner cartridge with wires and powder. It was discovered aboard a plane in East Midlands, north of London.

One official said intelligence personnel had been monitoring a suspected plot for days. The packages in England and Dubai were discovered late Thursday after a foreign intelligence service picked up information related to Yemen and passed it on to the U.S., this official said.